Fig. 2.

Simulated mass-density perturbations at the altitude (z) of 300 km as a function of time and horizontal distance from the center of the source (x). Up to 800 km, waves have horizontal phase velocities of about 220 m/s on the line “a”, 250 m/s on “b”, 300 m/s on “c” and 490 m/s on “d”, and horizontal wavelengths of about 200 km on “a” and 400 km on “c”.